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Injury and Yield Responses of Spinach Cultivars to Chronic Doses of Ozone in Open-Top Field Chambers¹

ABSTRACT

Spinach (Spinacia oleracea L.) cultivars were exposed continuously during growth to carbon-filtered air or nonfiltered ambient air in open-top field chambers. Constant low concentrations of ozone (O₃) were added to the varying ambient concentrations in the nonfiltered-air chambers for 7 hours (0920 to 1620 EDT) per day. There were significant differences in the amount of foliar injury and shoot growth decrease among 11 spinach cultivars exposed for 7 hours/day to 0.13 ppm of O₃; America, Winter Bloomsdale, and Seven-R were less sensitive to foliar injury than Chesapeake, Hybrid-612, and Dixie Market. Shoot growth of America and Viroflay was affected less and Hybrid-612 and Dark Green Bloomsdale more than that of most other cultivars. The cultivars America, Winter Bloomsdale, Hybrid 7, and Viroflay were exposed for 38 days to determine threshold doses of O₃ for injury and yield effects. The threshold 7-hour/day mean O₃ concentration for foliar injury was between 0.02 and 0.06 ppm. The threshold for a significant decrease in shoot growth of most spinach cultivars was between 0.06 and 0.10 ppm. Shoot fresh weights of plants grown in the ground at 0.06, 0.10, and 0.13 ppm were 18, 37 and 69% less, respectively, than plants grown at 0.02 ppm. Comparative values for potted plants grown in a 1:1:1 mixture of sand/soil/Pro-Mix BX were 4, 25, and 65%, respectively.

Key Words: oxidants • plant growth

¹ Cooperative investigations of the USDA and the North Carolina State Univ. Paper no. 5516 of the Journal Series of the North Carolina Agric. Exp. Stn., Raleigh, NC 27650.

² Plant Pathologist and Agricultural Engineer, respectively, SEA-USDA, Plant Pathology Dep., North Carolina State Univ., Raleigh, NC 27650; and Research Assistant, Plant Pathology Dep., North Carolina State Univ.

³ The authors thank Hans Hamann and J. P. Bennett for statistical analyses and Suzanne Spencer, Madeleine Engel, and John W. Johnston for their technical support.

Received for publication May 8, 1978.